How long were you laid up by the chest thing?
How far along in the program were you?
The second question will help inform the first.
I also just recently got over bronchitis brought on by the bad pollen situation in my area this spring. The major symptoms kept me out of the gym for two sessions. You’ll find your breath/condition will be knocked down some, but will be back within a week.
10% is probably OK enough, depending on above. Also, titrate the volume back up on your squats from one set, to two, and then three. PPST3 has a section on returning after layoffs.
As for being 17 and not being able to put on weight, the usual response is you are likely not eating as much as you think you are. This is typical for 17 year olds. Actually tracking your intake with accurate quantities may be revealing.